The present invention relates, in general, to material handling equipment and methods; and more particularly, it relates to apparatus and method for assembling wooden pallets of the type which are used for shipment and storage in many industries, such as the beverage industry, where goods are stored on a pallet and a load of goods is moved along with the pallet by means of a fork lift truck or the like.
Pallets are made in a variety of ways. Some of them are made completely by hand without even the simplest jigs or fixtures for assistance. Others are made by complex and very expensive machinery which not only feeds the deck boards into place, but automatically nails top and bottom deck boards in a single pass. Such machinery is obviously advantageous, but it is also so expensive that it is impossible to purchase for many manufacturers desiring to make pallets.
Pallets typically include three longitudinal members or "stringers." These are stronger members, typically made of 2.times.4 lumber. Two of them are located adjacent opposite edges of the finished pallet (they need not be flush), and the third is placed in the center. Upper and lower deck boards are fastened, preferably with nails, to the stringers. The deck boards extend transverse of the longitudinal direction of the stringers.
Pallets which are intended to be used in the heavier industries, such as automotive and the like, or in the beverage industry, are normally required to support heavy loads, and typically they are made of hard wood. Hence, an individual pallet which is 48".times.48" may weigh as much as 100 pounds or more. Further, the pallet industry in the United States is characterized by many different sizes and designs for pallets.
The present invention, then, is directed to a machine which is both economical to make and easy to use in assembling pallets, and which combines the lower cost, reliability and accuracy of hand nailing with the advantages of machinery in supporting the components of the pallet during manufacture and discharging a pallet after completion in such a manner that the operator never has to lift a completed pallet.
Briefly, according to the present invention, a cradle is mounted on a frame for pivotal motion about a horizontal axis between a starting position (in which the top of the cradle extends in a horizontal plane) and a discharge position in which the cradle is rotated 180.degree. about its rotational axis so that it is completely turned over.
The cradle includes a generally rectangular peripheral frame with a plurality of longitudinal guide bars extending between and supported by opposite ends of the peripheral frame. These bars extend in planes perpendicular to the axis of rotation of the cradle. At one end of the cradle, a linear actuator, such as an air cylinder is mounted between the peripheral frame and a clamping bar.
To commence operation, the clamping bar is retracted, and the cradle is placed in the start position. Stringers are placed in the cradle resting on the longitudinal guide bars and located by means of stringer guides carried by the guide bars. These stringer guides may be adjustably mounted to the guide bars so that pallets of different size or design may be accommodated by the apparatus.
After the stringers are inserted, the pneumatic cylinder is actuated (preferably, two such cylinders may be used) to clamp the stringers longitudinally. Means may be provided for locking the cradle relative to the frame at this time.
When the stringers are clamped in place, the operator places what will eventually be the bottom deck boards in their final positions across the stringers. These deck boards may be placed according to markings on the cradle. The bottom deck boards are then nailed to the stringers.
The cradle lock is then released, either pneumatically or manually, and the cradle is rotated 180.degree. so that the bottom deck boards are now beneath the stringers. This is the discharge position. When the cradle is thus turned over, the guide bars which originally had supported the stringers are then above the stringers, and they act as guides for locating the center top deck boards. The top deck boards at the ends may be placed flush against the opposing stringer clamp surfaces. The cradle is, of course, latched in this position also.
The top deck boards are then nailed to the stringers, thereby finishing the pallet.
When the pallet is completed, the clamp is released and the pallet is discharged from the cradle under gravity, the top deck boards falling free of the longitudinal guide bars which originally supported the stringers. The pallet may be discharged onto a conveyor or other mechanism for transporting it to storage or to a stacking machine, if desired.
With the present invention, semi-skilled personnel can complete the assembly of a pallet in less than a minute using pneumatic hand nailers commercially available. In relation to the cost of the machine, this is a substantial advantage over other pallet machines commercially available, and certainly over complete hand assembly of pallets, even using pneumatic nail guns. Further, the apparatus does not require operating personnel ever to lift a completed pallet. This is a considerable advantage when it is considered that each pallet weighs over a hundred pounds and that over 450 pallets can be made in a single day.
As will be more fully understood from the following description, the apparatus is fully adjustable for pallets of different length and width, as well as different designs (that is, different numbers of top and bottom deck boards).
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.